Distributed computers are used in printing presses both for making adjustments and for measuring parameters which can be used as the basis for making adjustments, throughout the press. Such distributed computers often find use in rotary printing presses, and such presses are often broken down into press units which localize the control mechanisms and measuring transducers at the various units. Thus, it is possible to associate a computer with each unit, or alternatively, to allow a single computer to service multiple units. However, in either case, the stations to be controlled (and from which measurements are taken), e.g., the press units, are usually at a distance of several meters or more from the computer. The length of wire runs between the computing equipment on the one hand and the actuators or transducers on the other hand can tend to introduce noise and interference problems which can render measurements taken undesirably inaccurate. In addition to noise problems, there is also a wiring density problem which is often encountered in highly automated presses. For example, if the distributed computer is to control ink feed, it may have as many as 20 and perhaps up to 54 ink adjusters per printing unit, and each of those adjusters require separate control lines and a separate signal line for an associated transducer.
Thus, automation of multiple unit presses can give rise to substantial control problems, which can involve not only the long cable runs (which give rise to the possibility of interference, perhaps on a random and uncontrolled basis), but also the high density of cable runs which can exacerbate the interference problem. In addition, in many highly automated press systems, it is often required for measurements, adjustments and control operations to be performed very fast. As an example, there are certain closed loop systems which are utilized, (as well as other non-closed loop systems) which attempt to make small corrections but with sufficient rapidity to maintain printed accuracy to within a few percent. When it is considered that there are a large number of controllable actuators on such a press, that each of the actuators can have a feedback mechanism associated therewith, that all of the feedback mechanism need be monitored, and that any or all of the adjusters might need readjustment at any given time, it will be appreciated that the addressing, signalling, control and measurement problems can become quite complex and inter-related.
A number of partial solutions have been proposed in highly automated printing presses. Those have included the use of expensive shielded cable for particular signal and control lines. Such cable requires special terminators and often special workmen for installation and maintenance. Other approaches have been taken in both hardware and software in order to make more manageable the signalling and integrity of signalling problem in large highly automated press systems, but those systems have not always been adequately simple in implementation, inexpensive in cost, or reliable in operation.